347. Top K Frequent Elements

Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.

Example 1:
Input: nums = [1,1,1,2,2,3], k = 2
Output: [1,2]

Example 2:
Input: nums = [1], k = 1
Output: [1]

Constraints:
1 <= nums.length <= 10**5
-10**4 <= nums[i] <= 10**4
k is in the range [1, the number of unique elements in the array].
It is guaranteed that the answer is unique.

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